With its initial public offering coming up later this week, Zynga is making a few notable traffic gains on Facebook and mobile. Older games like FarmVille are growing, not just new ones like CastleVille. The obvious reasons include it doing more advertising and cross-promotion — and getting some extra publicity out of new launches and media events.

But it looks like there’s more going. Facebook appears to have made a few adjustments to how users see app activity within the last month or so.

One way is that stories from apps are now appearing as individual items within the news feed. They’d previously appeared as bundles, with one story from the app at the top and the rest threaded underneath. Facebook had moved apps into this format more than a year ago in reaction to the spammy feeling that over-sharing apps had created. But it had a secret whitelist to let some apps from Facebook page service providers through. The unbundling could mean the company feels more comfortable with the current design and how news feed spam is handled within it. It could also be because Facebook is trying to increase growth for third party developers.

Zynga benefits from this type of change, because it’s so big that it receives a disproportional share of the results — and because it has built its organization around being able to react and optimize these types of changes quickly.

There could be another platform benefit happening, too. Facebook has also been showing a much higher number of notifications about individual apps in the past month, too. Anecdotally, I’ve noticed at least a couple invites a day from friends playing social games recently, whereas I’d had fewer in past months. The reason, my former Inside Network colleague and serious social-game-playing journalist AJ Glasser observes, is that Facebook has ungrouped these notifications. They’d previously appeared bundled up, which had decreased their visibility to players and non-playing friends.

Facebook has also adjusted how requests appear in the left-hand navigation bar, she notes. Individual app requests are now ordered by recency, with the generic “Game Requests” tab moved from the top of the requests section to the bottom.

While these changes appear to be helping Zynga, that’s not the whole story. Facebook app growth has been relatively weak in the past year or so, and many developers have been looking to mobile platforms instead. All of the changes above could help Facebook keep developers more focused on its platform.

[Update: Facebook spokesperson Malorie Lucich told me the following about the changes: “These communication channel updates are part of ongoing tests we’re conducting to drive traffic to apps and surface the right apps to the right people. Growth for apps of all sizes is an important focus for us and we will continue to test how to make Platform most effective for both developers and users.”]

Here are the Zynga games seeing big gains, from AppData. The company has overall grown by nearly 1.5 million DAU in the past couple weeks to nearly 51 million. It has also gained around 20 million more monthly active users, to reach 223 million. The numbers below are for DAU, as they more closely indicate engagement and revenue as well.

CastleVille, which has been growing fairly slowly since launching earlier.